Ion chromatography is widely used in the analysis of samples containing anions or cations. A typical process begins with introducing a sample in the solution of a conductive eluent, and then sequentially goes through chromatographically separating sample ions in the eluent, suppressing the eluent to remove the electrolyte counter ions to the sample ions, and detecting the sample ions. The purpose of suppression is to reduce the background conductivity of the eluent and increase the conductivity of the analytes, thus increasing the response in the subsequent detection.
Various suppressors are known and can be used for suppressing the eluent. Examples include those disclosed in U.S. Pat. No. 4,999,098, U.S. Pat. No. 6,328,885 and U.S. Pat. No. 7,618,826. In these suppressors, suppression is achieved by flowing the eluent through an eluent channel and a regenerant through a regenerant channel, where the eluent channel is separated from the regenerant channel by a charged membrane. The eluent and regenerant channels are defined by gaskets and rely on the gaskets for liquid-tight seal. Similarly, U.S. Pat. No. 6,752,927 discloses a salt converter device that uses gasketed screens and U.S. Pat. No. 6,808,608 discloses water purification devices that use gasketed screens. The gaskets are typically made of elastomeric materials, such as polyurethane or flexible liquid silicone-based rubber, set in place by press or UV initiated curing process.
Under certain circumstances such as an extreme pressure or temperature or upon long term usage, using gaskets to define and seal the eluent and regenerant channels may adversely affect the life time of these devices and in some instances chromatographic performance such as backpressure, noise performance, and peak band dispersion. For example, as the elastomeric gasket is compressed for seal, the overall forces tend to squeeze the gasket outward into the open area, for example, eluent and regenerant channels, over time. In some cases, such change generates significant backpressure and clogging in fluidic channels and causes leakage. In some cases, the gaskets are thinned out significantly due to the compression forces and no gasket is available in place to make a proper seal. Further, the force per unit area decreases over time as the gasket material is compressed, requiring significant torque optimization to overcome such change. In addition, exposure to higher temperatures may result in higher levels of leachates or melting of the gaskets which affects the noise performance or flow properties and in some cases may irreversibly damage the suppressors. Prior art devices also have the gasket as an integral part of the screen (i.e., gasketed screen) where the screen area is at least slightly larger than the channel and partially embedded into the gasket. This means that the access of the eluent to some areas of the screens is slow due to diffusion limitations. For example, the area close to the gasket edge defining the eluent channel fluidic pathway exhibits this diffusional limitation. The net effect of this behavior is that when the screen form is changed from one form to another (e.g., hydronium form to sodium form) there is slow diffusion of the reagents from within the gasketed screen to an open area away from the gasket edge. In another example when a cation exchange screen gasket was exposed to base eluent without any power applied to the suppressor the screen gets converted to the sodium form. There can be slow diffusion of sodium into the screen area located underneath the gasket proximate to the gasket edge. Upon resuming normal operation the peak area remains small until all of the sodium diffuses out of the gasketed region of the eluent channel. This is a slow process. In other instances when pursuing a high to low ratio of analyte analysis the slow diffusion of analyte can cause peak shape issues. Although many of the above problems could be circumvented by operating in a narrow operational regime in terms of pressure, temperature, concentration this imposes constraints from an operational perspective.
Conventional suppressors may have other limitations. For example, conventional suppressors incorporate fluidic geometries having different areas for the regenerant and eluent channels, thus the sealing across the channels are not uniform. Further, conventional suppressors incorporate a fluidic pathway design that routes eluent flow to the eluent channel via the regenerant gasket. This imposes the need to align the inlet and outlet of the eluent flow gasket with the through holes of the regenerant gasket during assembly and maintain the alignment over time. A slight alignment offset can result in high backpressure as well as poor peak shapes
In light of the above, it is desirable to provide improved devices that overcome at least some of the above-mentioned challenges of devices that use gasketed screens.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.